speaking of the mouth

my dad gets a good ole days type publication and in it they give old treatments for various maladies. recently his mouth has been in bad shape as far as his gums were concerned. he ran across an old remedy of swishing pepto-bismol in the mouth and spitting it out just before bed. he has been doing this lately and his gums have grown back and teeth have firmed up in their sockets. he is 73. he says that when he wakes up in the morning he has little black specks in his mouth when he rinses. he says they are like finely ground coffee.

not something i would chose to do, but one is hard pressed to knock success. its the saccharine and artificial colors that bother me. he doesnt use much, however, just enough to coat the inside of the mouth and spit the rest out. it works for him.

anybody care to guess why or what action is forming the black particles?